Maybe, if it's just Bass and Drums that disappoint, a couple of modules from another manufacturer would give a better change of timbre than another from the same?

I've heard of some using Roland TD-series drum modules on arrangers, for that G70 'live drum' sound (it's what's built-in to a Roland G70/E80) and there ARE some bass sounds built in to those... Perhaps they might suit you enough if added alongside the Yamaha basses.

Having auditioned MotifES and XS, I must say I thought their contemporary drumkits to be VERY good, but I wasn't as impressed with their acoustic kits as much as the TD-type G70 sounds... What type of drum sounds are you primarily looking for?